You have to remember that his character was raised since he was like 6 to be what he is: an elite soldier. Leading and fighting is what he knows. You also have to remember that for all he knows, all his buddies he trained with, they're all dead. Nearly everyone he cares about, gone. You don't suppose that might be something to kill emotion a little bit? Maybe all that's left for him is to finish the fight against the covenant, and as a disciplined soldier, he's a man of action, not words. And as a leader, your emotions are controlled, as your emotions affect the morale of the team. And he's not completely devoid of feeling. He went back for Cortana, didn't he? Anyhoo, bungie did a terrible job of actually conveying all this upon you people, but it's all there between the lines. He is badass. But a lot of his success is luck too.